1. Field of the Invention
The present invention relates to a map generation device that generates a map by extracting a polygon shape of a building roof from an aerial photograph (a photograph taken from a satellite or an airplane).
2. Description of the Related Art
Up to now, examples of a method of generating a map from an aerial photograph include a method of using an analytical plotter to manually trace a polygon shape of a building shown in an image, and a method of automatically extracting a building polygon shape from an image.
In the method of using an analytical plotter, two images photographed with parallax are estimated and aligned to generate a stereo image. Then, an operator extracts a building polygon shape from the stereo image by a handle operation (see, for example, Ujihisa Kimoto, Practice Of Photogrammetry, Sankaido. P.91-97).
Meanwhile, in the method of automatically extracting a building polygon shape, a monocular image is used along with information including a position, an angle, and a sun direction where the image was photographed to extract regions of a rectangular roof, a wall, a shadow, and the like based on linearity and positional relationships involved in information on lines extracted as edge images. Thus, existence of a building can be discriminated. For example, there is proposed a method of extracting a rectangular roof shape by setting information on the position, the angle, and the sun direction where the image was photographed as known conditions, and tentatively setting a building structure based on the line information obtained from the edge images (see, for example, C. O. Jaynes, two others, “Task Driven Perceptual Organization for Extraction of Rooftop Polygons”, Proceedings of ARPA Image Understanding workshop, 1994, P.359-365). There is also proposed a method of extracting stereo information on a rectangular building by setting information on the sun direction and a camera orientation where the image was photographed as known conditions, and discriminating local characteristics, relative positional relationships, and the like involved in the line information of a roof, a wall, and a shadow (see, for example, C. Lin, one other, “Building Detection and Description from a Single Intensity Image”, Computer Vision and Image Understanding, Vol.72, No.2, November 1989, P.101-121).
According to the above-mentioned conventional method of generating a map using an analytical plotter, extraction of a building polygon shape is conducted by the operation of an operator, making it difficult to correctly trace the building polygon shape. Further, the above-mentioned conventional method of automatically extracting a building region can be applied only to a building whose roof shape has a simple structure such as a flat roof shape. The building region cannot be extracted when sunlight falls on a roof such as a gable roof at different angles, producing gray contrast, or when a building has a structure such as an exhaust tower on its roof.